1. Field of the Invention
The present invention relates to a screw-type fastening device such as a bolt and nut, a bolt, casting screws, and the like and, more particularly, to a combined male and female threaded elements assembly which is shaped to swage crests of mating internal threads and thereby provides an interference fit and prevailing torque that resists self-loosening and protects the internal threads from abrading when the fastened male and female threaded elements are separated from each other.
2. Description of the Prior Art
Many fastening devices such as a bolt and nut known in the art include many types of continuous helical external and internal threads, such as for example, triangular or rectangular thread configurations. Such fastening devices are shown in U.S. Pats. Nos. 1,075,310 to Ulrich, No. 2,215,770 to Sheffield, No. 3,661,194 to Macfarlane et al, No. 4,023,914 to Holmes, No. 4,171,012 to Holmes, No. 4,341,497 to Downey et al, No. 4,432,682 to McKewan, and No. 4,600,224 to Blose. However, there are many problems with the prior art fastening devices. For example, it is difficult to tightly fasten them and it is easy to loosen them after fastening when the apparatus using such fastening devices is subjected to continuous vibrations, movements and/or impacts because the male and female threaded elements are shaped with different configurations. Also such fastening devices cannot prevent abrasion of the threaded portions when the fastened male and female elements are separated from each other.